This invention teaches a particular set of additives that when added to fully formulated engine oil, as used in internal combustion engines, which additives reduce timing chain wear. In particular, this invention teaches the use of zinc dialkyldithiophosphates (ZDDP) used in combination with A) ashless alkyl dithiophosphate ester, B) an alkylphosphate alkylammonium salt, C) a molybdenum-containing friction modifier or D) any combination of A, B and C, in a fully formulated engine oil. The invention also contemplates a lubricant, which is substantially free (i.e. <1 ppm zinc) of ZDDP, and containing an additive selected from one or more of A-D above. In addition, the invention teaches methods for reducing timing chain wear by using lubricating composition formulated as above, as well as a system including an engine having such a lubricating composition in contact with the timing chain present within the engine (e.g. internal combustion engine).
Governments around the world have passed legislation requiring automobile manufacturers to improve vehicle performance with respect to reducing greenhouse emissions and improving fuel efficiency. To meet these tough targets, automobile manufacturers have introduced new engine technology. One new engine technology recently introduced is the turbocharged direct injection engine (“T-GDI”). Unfortunately the T-GDI engine is experiencing higher than normal timing chain wear. The automobile manufacturers judge the timing chain wear problem to be such a significant concern that the next generation passenger car motor oil specification is expected to have a timing chain wear engine test as part of the specification.
A timing chain is composed of links and pins. The pin is used to hold two chain links together and the chain links are the building blocks of the timing chain. When the automobile's engine is running, the timing chain link pivots around the pin as the chain is pulled by the gear teeth. Wear occurs on the inside of the link aperture by the action of the pin articulating against the link aperture. This wear action causes the link aperture to enlarge over time and the pin to reduce in diameter. Chains become elongated as the numerous joints of the chain wear. The timing chain coordinates the opening and closing of the intake and exhaust valves with respect to piston position. The intake valves allow fuel into the combustion chamber and the exhaust valves allow for the discharge of the spent combustion gases. If the timing chain becomes sufficiently elongated such that it no longer stays in place and consequently jumps a sprocket tooth the timing for the opening and closing of the intake and exhaust valves with respect to the piston moving up and down in the cylinder is disrupted to the point of improper engine combustion.
Timing chains operate in a severe environment inside an engine. Because of this, it is a common practice in the industry to coat the timing chain to protect it. Non-limiting, examples of coatings include: nitride coatings such as carbonitride, titanium nitride and chromized coatings, and carbide coatings such as vanadium carbide.